This invention relates to multi-axled traction vehicles, and more particularly it relates to means for detecting a locked axle condition on such a vehicle.
A traction vehicle such as a railway locomotive has a plurality of axles for driving the wheels of the vehicle along a track. In operation one of the axles may become locked against rotation due to seizure of bearings or the like. If this condition were not promptly detected and corrected, it could have a number of adverse consequences, including the wearing of flat spots on the wheels. In order to minimize such difficulties, it is desirable to warn the engineer of the locomotive that a locked axle of a sliding wheel condition has occurred.
Accordingly, a general objective of the present invention is to provide an improved scheme on a multi-axled traction vehicle for detecting when one or more (but less than all) of the axles are locked.
As will be hereinafter described, the present invention has the capability of detecting a predetermined speed differential between axles which are rotating at different rates. Therefore another possible application of this invention is to detect an untoward increase in the speed of one axle due to a wheel slip condition. It has heretofore been proposed in the wheel slip art (see U.S. Pat. No. 3,699,563 granted on Oct. 17, 1972) to separately sense the speed of each drive axle of a locomotive by means of a magnetic proximity detector mounted adjacent to the teeth of a gear which rotates with the axle, thereby producing a periodic signal whose frequency varies with the rotational speed of the axle, which signal is then converted to an analog signal proportional to frequency. The analog signals from the speed sensors associated with the respective axles of the locomotive are compared with one another, and an output is produced whenever the difference between the signals of least and of greatest magnitudes exceeds a predetermined amount which corresponds to an intolerable difference between the slowest axle speed and the fastest axle speed of the locomotive.
The use of magnetic proximity detectors to detect the speed of rotating parts or apparatus is well-known in the traction vehicle art. Such a detector has many advantages, including relatively low initial cost and maintenance expense and high reliability. There are, however, a few shortcomings. The amplitude of the signal produced by a magnetic proximity detector tends to vary with frequency and depends on the distance or air gap separating the pickup head of the detector from the surface of the adjacent gear teeth. The minimum speed sensitivity of such a detector is also a function of the aforesaid gap. Where a constant, predetermined amplitude is desired, the output of the detector can be connected to an operational amplifier or the like, as is known. But this does not solve the pickup sensitivity problem, which makes it difficult to apply magnetic proximity detectors in a locked axle detecting scheme where response to axle speeds close to zero is required.
Accordingly, another general objective of the present invention is to provide an improved axle speed differential detecting scheme which can utilize speed sensors having inprecise and possibly unequal pickup sensitivities and which nevertheless is suitable for locked axle detection purposes.
A further object is to provide an accurate speed differential detecting scheme utilizing parts and circuit components which separately have relatively wide tolerances.
Yet another object is the provision of a system for detecting a predetermined speed differential among a plurality of axles on a traction vehicle wherein the need for precision adjustments of the system is minimized in the event components are replaced or the wheels wear unequally.